Cast valve seat made of an iron alloy



Sept 10, 1957 H. F. PRASSE ET AL 2,395,943

CAST VALUE SEAT MADE OF AN IRON ALLoY Filed 001.. 7, 1954 fig. 3

1 12a 12a J3 fig-4' i Q. ////Am|m 19 1762556 I e/7665 flo/v/i X. leusreoma United States Patent 2,805,943 CAST VALVE SEAT MADE or AN IRoN ALLoY Herbert F. Prasse, Gates Mills, and Adria A. Armstrong, Mentor, Ohio, assignors to Thompson Products, lne, Cleveland, Ohio, a corporation of Ohio Application October 7, 1954, Serial No. 463,846

4 Claims. (Cl. 75-426) The present invention relates to valve seat inserts of the type employed in internal combustion engines.

While the valve seat insert is a relatively simple structure from a mechanical point of view, the metallurgical problems presented in attempting to provide a completely suitable valve seat insert for modern engines employing leaded gasolines are very substantial.

One of the primary problems of the selection of a suitable metal or alloy for use in valve seat inserts arises from what is known as collapse resistance.

It is known that when metals or alloys are heated to very high temperatures for extended periods of time, they will congeal or set in an expanded state and will not contract to their original dimensions when cooled. Since engine valve seat inserts are normally press-fitted in recesses in engine cylinder heads or blocks, the valve seat inserts become heated in the operation of the engine and may expand to a point where further expansion is restricted by the cylinder metal itself. When this point is reached, continued expansion due to increased temperatures will cause the insert to bow inwardly away from the restraining shoulder or wall of the engine head or block. If the bowed inserts reach the setting temperature and are then cooled from this temperature, the insert metal shrinks away from the insert recess and the insert becomes loose in the engine. The bowed and set inserts are known as collapsed inserts and the temperature at which such inserts take a permanent set is known as the collapsed temperature.

In the past, valve seat inserts for the most part have been produced by expensive forging, machining, and heat treating procedures. The best of these prior known inserts had to be annealed, hardened, quenched, tempered, and drawn to a Rockwell hardness of about 35 on the C scale. exhibited an aggregate of carbides with some martensite oriented in an interdendritic pattern and having some of the carbides in the grain boundaries and scattered throughout the matrix. This structure, however, did not provide adequate collapse resistance at temperatures above about 800 F. Since modern, high speed, high compression internal combustion engines frequently operate at temperatures which would cause the temperature of valve seat inserts to rise to above 800 F. collapsed inserts have presented a serious engine problem.

Another problem which manifests itself particularly in engines employing gasolines having a relatively high percentage of tetraethyl lead is that of surface resistance. a' good insert must have a smooth face which resists depositbuild up, corrosion, erosion, pitting, or exces sive wear. Otherwise, an unsatisfactory seal will result between the valve seating face and the valve seat insert ring.

A characteristic possessed by a good valve insert ring is that of lack of atiinity for the carbonaceous materials and lead deposits present in the combustion chamber. These materials tend to become deposited on valve seat The micro-structure of these inserts generally "ice 2 insert rings and act as efiective heat dams, thereby increasing the valve head temperatures.

In line with the above, a good valve seat insert should also maintain its hot hardness properties, i. e., it should retain a substantial amount of its hardness even at the elevated temperatures at which the engine is operating. This ability to maintain its hardness governs to a large extent the degree of contact which can be maintained between the valve face and the valve seat insert at the operating temperatures of the engine.

The characteristics of the valve seat insert also have a pronounced effect upon the valve lash changes evident during operation of the engine. These changes accumulate in the valve train due to wear and the pounding down of the valve seat insert during use. It is desirable that the valve seat insert have characteristics which minimize these changes, as it is undesirable to make frequent adjustments on the valve lash during operation of the engine.

All of the above factors indicate that the problem of selecting a suitable alloy for valve seat insert rings is quite substantial.

In view of the foregoing, the need still remains in the art for a more satisfactory valve seat insert ring, and the satisfaction of that need is the primary object of the present invention.

Another object of the present invention is to provide an improved valve seat insert ring which is less expensive and more convenient to manufacture than the type of valve seat insert rings being presently employed in many types of internal combustion engines.

Other and further objects of this invention will b apparent to those skilled in the art in the foregoing 'detail description of the annexed sheet of drawings which, by way of example only, illustrates a valve seat insert of this invention.

On the drawings:

Figure 1 is a plan view of the valve seat insert ring of the present invention;

Figure 2 is a fragmentary view, with parts in elevation, of the valve port area of an internal combustion engine, showing the valve seat insert in its normal condition;

Figure 3 is a greatly enlarged fragmentary view of the valve port area, illustrating the insert ring in its normal condition;

Figure 4 is a view similar to Figure 3, but illustrating the ring in its collapsed condition;

Figure 5 is a graphic reproduction of a micro-structure of the alloy constituting the insert, at a magnification of about 500 times.

As shown on the drawings:

From Figures 1 to 4, it will be seen that the engine valve port assembly 10 may include an engine block or cylinder head 11 normally composed of cast iron, and a cast valve seat insert 12 press fitted into 'a recess 13 of the engine block or head 11. A bore 14 concentrio with the recess 13 is provided to receive a valve stem guide 16 in the usual manner. A valve 17 is shown in seated relation in the valve seat insert ring 12 (Fig. 2), the valve 17 having a stern 17a slidably received within the valve stem guide 16.

The valve seat insert ring 12 may consist of a ring having a cylindrical outer peripheral wall 121:, a flat bottom 12b, a flat top 12c and a tapered seatingface 12a converging from the fiat top to a cylindrical inner peripheral wall 12c.

The peripheral wall 12:: is in snug fitting relation with the vertical wall of the recess 13 and is preferably press fitted or shrinkiitted into the recess 13 with the flat bottorh 12b of the insert being" seated upon the bottom of tungsten are substantially interchangeable.

the recess 13. As evident from Figure 2, the tapered seating face 12d is'arranged to receive the tapered seat 17b on the valve 17.

In normal operation, .the valve seat insert ring 12 main: tains its tight fit in the recess 13 and expands to substantially the same degree as the metal in. which the recess 13 is formed. However, when the valveseat insert 12 is heated to :a point where it can expand no further due to the restraining efiect of the walls of the recess, it may become bowed as illustrated in Figure 4. This bowing may create agap illustrated at 19 in an exaggerated form in Figure 4. If the insert 12, is col lapsed in the condition shown in Figure 4,'then the gap 19 will remain void under lower operating temperatures. As aresult, the insert 12 willremain loose inthe recess 13. We have nowfound that the collapse temperature of valve'seat inserts 'can'be increased and other desirable properties of the inserts enhanced by employing a cas valve seat insert having the following composition:

. 7 Percent Carbon 2.25 to 2.75 Chromium 27.0 to 33.0 Cobalt 10.0 to 14.0 Tungsten, molybdenum or mixtures thereof 5.0 to 7.0

Iron; substantially the balance.

For the purposes of this invention, molybdenum and Where the hardness of the insert is of prime importance; tungsten alone may be employed, but where toughness is the objective molybdenum alone will be used. If desired, a mixture of the two metals may be used to secure the benefit of both metals. 7,

A particularly preferred composition for valve seat insert rings is the following:

Percent Carbon 2.5 Chromium 30 Cobalt 12 Molybdenum 6 Iron, substantially the balance.

- Another preferred composition having particularly good strength properties is the following:

Percent Carbon 2.70 Chromium 29 Cobalt 10 Tungsten 7 Iron, substantially the balance.

The alloys of the above compositions may be melted and cast in suitable molds for producing the insert ring 12. The casting process employed may include conventional sand casting, shell molding, investment casting or other casting techniques capable of producing smooth, accurate castings free from cracks, blow holes, shrinks, and the like. Y

The cast insert rings need no special heat treatment, making them considerably easier. and less expensive to manufacture than commonly used insert rings which require hardening and drawing steps incident to their manufacture;

The microstructure of the finished valve seat insert rings is illustrated in Figure 5 of the drawings. It will be observed thatthis structure includes relatively large dendrites 21 surrounded by a solid solution 22 consisting of a eutectic matrix. 7 I

A convenient collapse test for the rings consists in inserting the ring under test in a cast iron cup receiving a high frequency induction coil in the hollowinterior of the ring. The test iron cup is surrounded by a water ring. The insert is then intermittently heated by the induction coil and cooled by a water spray on the cast cup. The insert is heated first to about 300 F. for several hundred cycles of operation. It is then cooled and checked for looseness. The temperature is then raised in 25 increments and the heating is repeated for several hundred cycles. The procedure is continued until the insert under test loosens in the cast iron cup. The final temperature is then recorded as the loosening temperature or collapse temperature.

The collapse resistance of three insert rings having compositions within the ranges given previously was measured with the following results:

Initial Decrease Decrease Increase Cycles Final Inter- Insert, Insert, Fixture, to Tcmp., ference D. I. D I. D. Loosen F.

oxidizing atmosphere 1 hour at 1675 F. Sample #1 9.6 g./sq. dm. Sample #2 8.7 g./sq. dm. Sample #3 8.4 g./sq. dm.

Average 8.9 g./sq. dm.

In addition to the foregoing, valve seat inserts made in accordance with the present inventiondid not accumulate a significant amount of combustion chamber deposits on their faces and evidenced only a slight loss in hardness at the operating temperature of the engine. In most instances, there was no measurable change in the average hardness at the top of the insert, even after the insert had been employed for 400 hours of cyclic operation in a heavy duty gasoline engine. .'A very significant advantage of the present invention arises from the valve lash properties observed when valve seat inserts of the present invention were employed in operating engines. In one such test, a heavy duty truck engine was operated with several of its 8 cylinders employing valve seat insert rings of the present invention. In all cases, there was an increase in accumulated valve lash of 0.001 inch in those cylinders employing the alloy of the present invention. In contrast, a high nickel alloy containing 58.7% nickel, 26% chromium, about 4% iron, and 2.0% carbon exhibited a decrease of accumulated lash change in excess of about 0.010 inch for the same period of operation in the same engine.

From the foregoing, it will be appreciated that the valve seat inserts of the present invention have exceptional resistance to.collapse, resistance to lash loss, and excellent corrosion resistance. The additional properties of good hot strength and resistance to deposits make the alloys of the present invention considerably more satisfactory for the intended use than heretofore known more expensive insertsi I While the alloys of the present invention have properties making them particularly suitable in the manufacture of valve seat inserts, it will be appreciated that the alloy will have more general applicability to articles toquiring wear and corrosion resistance properties.

It will be understood that modifications and variations may be effected without departing from the scope and novel concepts of the present invention. 5

We claim as our invention 7 V V 1. A cast valve seat insert for an internal combustion Iron, the balance except for incidental impurities.

2. A cast valve seat insert for an internal combustion engine comprising a ring having the following composition:

Percent Carbon 2.5 Chromium 30 Cobalt 12 Molybdenum 6 Iron, the balance except for incidental impurities.

3. The method of making a valve seat insert having improved wear resisting properties which comprises forming a molten mixture having the following composition:

Percent Carbon 2.25 to 2.75 Chromium 27.0 to 33.0 Cobalt 10.0 to 14.0

Metal selected from the group consisting of molybdenum, tungsten, and mixtures thereof 5.0 to 7.0

Iron, the balance except for incidental impurities. and casting said mixture into the form of a ring.

4. The method of making a valve seat insert having improved wear resisting properties which comprises forming a molten mixture having the following composition:

Percent Carbon 2.5 Chromium 30 Cobalt 12 Molybdenum 6 Iron, the balance except for incidental impurities. and casting said mixture into the form of a ring.

References Cited in the file of this patent FOREIGN PATENTS Great Britain Sept. 3, 1952 OTHER REFERENCES Steel Castings Handbook, 1st edition, page 287. Pub- I lished in 1941 by the Steel Founders Society of America, Cleveland, Ohio. 1 

1. A CAST VALVE SEAT INSERT FOR AN INTERNAL COMBUSTION ENGINE COMPRISING A RING HAVING THE FOLLOWING COMPOSITION: 